我一直认为这句话经常导致软件设计师犯严重错误，因为它已经被应用到了不同的问题领域。这句话的完整版是“We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil.”
We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil.
字面意思是97%优化是不值得也不应该做的，“过早”的那类优化是指这97%，关键点的优化，也就是剩下的3%仍是绝对必要的，虽然作者并没有直接说“这3%应该尽早做”，但某种程度上“we should not pass up our oppurtunities”大概已经包含了这层意思。作者并不反对优化，而且强调作关键优化的必要性。直白地说，他的意思是：不要浪费时间做那些根本不重要的优化。
Telnet is commonly used to check if a TCP connection to a specific port succeeds — essentially testing whether the port is open and reachable. Note that telnet itself is TCP-based, so it cannot test UDP sockets.
Quick background Telnet is the classic remote login client based on the TELNET protocol. It lets you run commands on a remote server as if you were sitting in front of it. You log in with username/password, but everything (including credentials) is sent in clear text — very insecure. Most modern Linux servers disable telnet and use SSH instead.
That said, curl can test HTTP services, and telnet can too (more on that below).
For UDP testing, use:
nc -u
nmap -sU
tcpdump
Application-level tools like dig for DNS
Common options
-4 Force IPv4
-6 Force IPv6
-8 Allow 8-bit data
-a Attempt automatic login (rarely used now)
-b<alias> Use alias for host
-e<char> Set escape character (default Ctrl+]) Example: telnet -e ^X host port
-l<user> Specify login user (for traditional telnet servers) Example: telnet -l root 192.168.1.10
-n<file> Log session to file (great for debugging)
In interactive mode After connecting, press Ctrl+] to enter telnet command mode. Useful commands:
quit Exit telnet
close Close current connection
status Show connection status
open host port Connect to new host/port
set localecho Enable local echo
toggle crlf Toggle CR/LF handling
Examples
Connect to a remote telnet service
telnet 192.168.120.206
(or by domain: telnet www.baidu.com)
If it fails:
Check IP/address
Is the host up?
Routing correct? (route)
Is telnet service running? (netstat -tlnp → look for TCP 23 LISTEN)
Firewall allowing port 23? (iptables -L)
Test TCP reachability (the 80% use case)
telnet 127.0.0.1 6379
Outcomes:
Connected → port open and TCP reachable
Connection refused → port not listening
Connection timed out → network/firewall issue
As a generic TCP client Telnet doesn’t care about application protocols — it just sends whatever you type over TCP. Perfect for quick testing of text-based protocols.
HTTP example:
telnet example.com 80
GET / HTTP/1.1
Host: example.com
(then hit Enter twice)
Redis example:
telnet 127.0.0.1 6379
PING
→ +PONG
Typical telnet service config (/etc/xinetd.d/telnet)
service telnet
{
disable = no
flags = REUSE
socket_type = stream
wait = no
user = root
server = /usr/sbin/in.telnetd
log_on_failure += USERID
}
You can use Tinker to verify if your database connection is working:
php artisan tinker
Then inside Tinker, run:
DB::connection()->getPdo();
If the connection succeeds, you’ll get back PDO instance details. If it fails, you’ll see the actual error message (usually something helpful like credentials issues or host unreachable).
